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CHRONIC DIETARY EXPOSURE WITH INTERMITTENT SPIKE DOSES OF CHLORPYRIFOS FALLS TO ALTER SOMATOSENSORY EVOKED POTENTIALS, COMPOUND NERVE ACTION POTENTIALS, OR NERVE CONDUCTION VELOCITY IN RATS.
Citation:
Graff, J. E., R S. Marshall, D L. Hunter, AND D W. Herr. CHRONIC DIETARY EXPOSURE WITH INTERMITTENT SPIKE DOSES OF CHLORPYRIFOS FALLS TO ALTER SOMATOSENSORY EVOKED POTENTIALS, COMPOUND NERVE ACTION POTENTIALS, OR NERVE CONDUCTION VELOCITY IN RATS. Presented at Society of Toxicology, Baltimore, MD, 3/21-25/04.
Description:
Human exposure to pesticides is often characterized by chronic low level exposure with intermittent spiked higher exposures. Cholinergic transmission is involved in sensory modulation in the cortex and cerebellum, and therefore may be altered following chlorpyrifos (CPF) exposure. This study examined the effects of chronic (1 year) dietary exposure (0, 1, or 5 mg/kg/day) to CPF in weight maintained (350g) male Long Evans rats (100-110 days old at study initiation) on somatosensory evoked potentials (SEPs). Peripheral compound nerve action potentials (CNAPs) and nerve conduction velocity (NCV) were also examined to differentiate possible changes in the central vs peripheral nervous system. The CPF doses were chosen to produce minimal and approximately 50% inhibition of brain cholinesterase activity, respectively. In addition to dietary exposure, half of the rats received an oral bolus of 45 mg/kg CPF (in corn oil) every other month (n = 16-17 rats/treatment). In order to examine only irreversible effects, the animals were tested 2.5 months after final exposure. Rats were implanted with screw electrodes over the cortex and cerebellum. One week later, unanesthetized animals were restrained and their tails inserted into a stimulation/recording device. Biphasic stimulation at 1, 2 and 3 mA was delivered via two pairs of stimulation electrodes (stainless-steel 25 ga needles) placed in the tail. Another pair of electrodes recorded the CNAP and NCV. The evoked responses showed the expected intensity-dependent changes in all treatment groups, indicating that the animals' responses were under stimulus control. Chronic dietary CPF (alone or in combination with spike doses) did not produce any irreversible changes in cortical or cerebellar SEPs, CNAPs or NCVs in adult animals. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.